Reigning in impulsivity
Interrogation of the interplay between the dopamine and serotonin systems underlying the development of impulse control disorders induced by dopamine replacement therapy
Up to 20 percent of people with Parkinson’s disease who take a new class of drugs to help reduce their stiffness, shakiness, slowness or unsteadiness have encountered an unwanted side-effect: impulsivity.
Although the drugs, ropinirole and pramipexole, are effective at reducing motor control problems, the unwanted impulsivity can lead people into destructive behaviours.
At the University of British Columbia, neuroscientist Melanie Tremblay is investigating the underlying mechanisms and pathways in the brain that are associated with the drug’s impulsivity reactions.
“People develop things like gambling, hypersexuality, binge-eating,” Tremblay explains. “It can be really devastating in those people.”
Ropinirole and pramipexole work by increasing the release of dopamine in the brain, and serotonin has been implicated in disorders of impulsivity, as well as in Parkinson’s disease. Tremblay is working with animal models to understand the interplay between these two systems in creating impulsivity in response to drug treatment for the disease. She’s also testing the effectiveness of another medication that works on the serotonin system, to see if it can reverse the unwanted impulsivity effects of ropinirole.
Her goal is to discover a way to either reduce or block the side effects of these useful medications, or to predict who might be particularly vulnerable to the side effects, for example people with less serotonin in their systems. Then doctors could avoid prescribing these drugs to those people.
“These drugs are actually very good,” Tremblay says. “When they work, they work very well.”
Alternatively, if Tremblay discovers that another drug could help, then doctors might be able to add it to a treatment plan to decrease these side effects.
Tremblay, who initially wanted to be a psychologist, fell in love with learning about receptors and cellular pathways when she took a course on the biology of the brain during her undergraduate degree.
“I always like learning about how drugs work,” she says. “They make me curious.”
During that research, Tremblay became interested in Parkinson’s disease—and now she hopes her work will lead to new treatment options for people with Parkinson’s.
Eventually, she’d like to become a professor or in working in drug development and drug testing.
“Right now, since there is no cure (for Parkinson’s), we have the option of giving levodopa or deep brain stimulation, which is really invasive. However I can improve those treatments—that’s my goal for now.”